Nicotine production from polyamine putrescine, a precursor of nicotine, can be produced by two pathways in plants. Putrescine can be synthesized directly from ornithine in a reaction catalyzed by the enzyme ornithine decarboxylase, or can be produced indirectly from arginine in a sequence of reactions initiated by arginine decarboxylase. The first committed step in nicotine biosynthesis is the conversion of putrescine to N-methyl putrescine by putrescine N-methyltransferase (“PMT”). N-methylputrescine is subsequently oxidized by a diamine oxidase, and is cyclized to produce a 1-methyl-Δ1-pyrrolium cation, which is subsequently condensed with nicotinic acid to produce nicotine.
There is a need for compositions and improved methods for genetically regulating the production levels of nicotine and other alkaloids in plants, including transgenic plants, transgenic tobacco plants, recombinant stable cell lines, recombinant stable tobacco cell lines, and derivatives thereof.